Sounds like your test kit is true since the other tanks readings are inline with normally recorded values. [smilie=nerd.gif] As mentioned I would check the alk level in newly mixed SW. Also keep in mind that different salts have different mixing criteria etc., so be sure your salinity is where it should be and not elevated. [smilie=nerd.gif] I still use reef crystals and have tried others. YMMV
Cheers,